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SubjectRe: Linux as a SCSI _Target_ device?
On Wed, Nov 11, 1998 at 09:23:20PM +0100, MOLNAR Ingo wrote:
> i'm not sure wether such a thing exists in retail, but you also need
> kernel support for this. The point would be to 'export' a block device
> (RAID5) as an SCSI target.

Exactly. And such a thing does exist in retail. It's apparently big
at this year's COMDEX. But sheesh, these drive towers are expensive.
Best price I have seen on a 5-drive IDE tower (no drives), fast SCSI
interface, is US$1600. A 10-drive tower is twice that expensive.

These folks are using ASICs or 486DX2-50 CPUs. A low-end Linux box
would probably do it faster.

I'd start working on kernel support for this if I had a clue on how
to approach it. At first glance it would appear that normal PCI SCSI
chips can't be used in this way ... but maybe they can. No data on
the Symbios web page, so...

> i was thinking about this one yes, this way Linux could be a real
> hardware-RAID box. It's _not_ really complex, but i havent seen this yet.
> The board has to do something like this:
>
> - send an IRQ if an SCSI command arrives
> - should be able to DMA out to the SCSI bus and also accept DMA
> transfers.
>
> probably there are some RT considerations (Linux has to react within a
> given timeframe), but maybe not, and Linux can sure can do much better
> than the millisec-timescale of RAID arrays. It is an interesting project.
> True 50-500G hardware-RAID for $5K or so.

One big problem is stuffing a lot of IDE interfaces in a linux box.
The hardware would be trivial (i.e. an 8-channel PCI IDE controller).
But it's not exactly an off-the-shelf thing.

Thanks for your comments!

Jeff

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